World’s Largest Vacuum Chamber Can Swallow Lesser Vacuum Chambers

Andrew Tarantola

The Space Environment Simulation Lab is a big vacuum chamber. Like, “able to swallow a Space Shuttle” big. Impressive, sure, but NASA’s Space Power Facility is an even bigger one. Like “can accommodate the entirety of the SESL with room to spare” sort of bigger.

Built in 1969, the Space Power Facility is located in Plum Brook Station, part of the Glenn Research Center in Cleveland, Ohio. At 37m tall with a 30m diameter, the SPF is the world’s largest vacuum chamber. It was originally commissioned to test the thermal vacuum readiness and electromagnetic interference resistance of both nuclear and conventionally powered spacecraft (though no nuclear tests were ever performed), high-energy experiments, rocket-fairing separations and the like.

However, it’s recently been renovated to test NASA’s new breed of spacecraft propulsion systems, such as those powering the new Constellation-class starship, Orion, as well as the airbag landing systems for the previous pair of Mars rovers. The chamber’s ability to faithfully reconstruct the conditions of space for these tests rests in its unique construction.

The SPF is essentially a huge aluminium silo wrapped in an even bigger concrete dome. The Aluminium Test Chamber is built from airtight Type 5083 aluminium plates — the same kind used to keep Walt Disney’s head on ice — that maintains the chamber’s frosty -195C temperature while maintaining a “low neutron absorption cross-section,” according to the space agency. Up to 300 tons of equipment can be loaded into the chamber via a 15m by 15m double-sealed door. The aluminium chamber also features an array of 4MW quartz heat lamps to mimic solar radiation and a 400kW arc lamp to replicate the solar spectrum.

Surrounding the Aluminium Test Chamber is the Concrete Chamber Enclosure (OK, so NASA’s not one for clever naming schemes). This structure measures 40m in diameter by 46m tall and is between 1.8m and 2.4m thick with an embedded steel containment barrier. This helps prevent both radiation from the quartz lamps from leaking out and natural radiation from leaking in. Altogether, the two structures can achieve 10^-6 torr of vacuum. That’s, what, roughly one hundred-millionth of a standard Earth atmosphere?

In addition to the original Test Chamber, NASA recently constructed a pair of new silos to ensure the Orion’s engines are both acoustic-ready and vibration-ready for their trip to the moon. The vibration testing facility is designed to reconstruct the violent shaking that a rocket endures during takeoff. It relies on a violently shaken 56,700kg suspended below a vibration table (what the equipment sits on).

“A rocket isn’t a very smooth ride,” said Jerry Carek, Space Power Facility Manager, in a press statement. “We want to simulate the vibration effects from the rocket engines that are going to launch it.” Shaking isn’t the only thing that the Orion will deal with during lift-off — the sheer noise from the engines is enough to damage the spacecraft’s delicate systems. That’s where the acoustic chamber comes in.

The new SPF acoustic chamber is the most powerful of its kind. It utilises 24 horns of various sizes (and frequencies) to match the racket of a launch and ensure that the massive sound waves generated don’t cause bolts to rattle loose. “The sound produced can be compared to putting your ear right next to a jet engine, just 10 10 times as loud,” Carek said. No word yet on what frequencies are actually used, though I’d like to think they sound like really loud vuvuzelas. [NASA 1, 2, 3 – Wikipedia]